Mamenchisaurus lived around 155 million years ago during a very warm and wet period of the Earth’s history.
This dinosaur may have had the longest neck of any other dinosaur. Many paleontologists believe that it used its massive neck to eat foliage on the ground. They believe that Mamenchisaurus would have swung its neck in a giant arc, eating everything it could eat. Then it would have taken a step forward, and started the process over again.
Scientists used to think that Mamenchisaurus lived in swamps, and floated its head at the top of the water where it could eat water plants. This idea is no longer accepted, however.